1. Field of the Invention
The invention relates to a manufacture method for a polymer electrolyte fuel cell (hereinafter, abbreviated as “PEFC”), and to the PEFC. More particularly, the invention relates to a manufacture method for a PEFC that has a protective layer in a unit cell structural body, and to the PEFC.
2. Description of the Related Art
Generally, PEFCs are roughly divided into two types, that is, a first type unit that is a basic unit that includes an electrolyte membrane, an anode catalyst layer and a cathode catalyst layer that sandwich the electrolyte membrane, and an anode diffusion layer and a cathode diffusion layer that are disposed on an outer side of the anode catalyst layer and an outer side of the cathode catalyst layer, respectively, and a second type unit that is a more industrial and practical unit that has a membrane-electrode assembly (hereinafter, abbreviated as “MEA”) in which an electrolyte membrane, and catalyst layers sandwiching the electrolyte membrane are integrated, and diffusion layers disposed on outer sides of the catalyst layers so as to sandwich the MEA. Then, a laminate that includes the component elements of the first or second type unit is hot-pressed so that the component elements are joined. Thus, a portion that corresponds to a unit cell structural body is fabricated.
In the second type unit (where an MEA is included), as for example, if a support of the electrolyte membrane is not provided on the inside of a gas seal member (protective layer) that surrounds a peripheral edge portion of the MEA in the manner or a picture frame, the differential pressure of the fuel gas or the oxidizing gas can sometimes break a peripheral edge portion of the MEA due to strain of a component element caused by the thermal stress or the mechanical stress caused by variation in humidity.
Japanese Patent No. 3368907 discloses a structural body 50 (that corresponds to a half of a unit cell structural body, and therefore will be referred to as “half-cell structural body 50”) which is made up of component elements as shown in an exploded view in FIG. 4A, and which is capable of preventing the damages to the electrolyte membrane caused by differential pressure or mechanism stress that acts on the electrolyte membrane. This half-cell structural body 50 is fabricated by superimposing an electrolyte membrane 1 on a carrier membrane 4, and superimposing a separately formed picture frame-shape protective layer 2 on a peripheral edge portion 1E (that includes a picture frame-shape portion of the electrolyte membrane 1 between the end portion and an imaginary dashed line S) of a surface 1S of the electrolyte membrane 1, and laying a catalyst layer (catalyst electrode portion) 3 on the picture frame-shape protective layer 2, and integrating the thus-laminated body by hot pressing.
Besides, Japanese Patent No. 3368907 also discloses a fluorine-based resin sheet of 25 μm in thickness as a membrane that corresponds to the protective layer 2. In the case where the protective layer 2 is a thick membrane, if the picture frame-shape protective layer 2 of 25 μm in thickness is hot-pressed to the electrolyte membrane 1, a large step is formed between the protective layer 2 and the electrolyte membrane 1, so that buckled sites occur in a peripheral end portion of the catalyst layer 3, and creep deformation of the electrolyte membrane 1 is caused. As a result, it becomes impossible to secure reliability of the fuel cell.
Besides, Japanese Patent No. 3690682 discloses an example in which a synthetic resin that melts at a processing temperature at which the picture frame-shape protective layer 2 is hot-pressed, for example, polyethylene, or an ethylene-vinyl acetate copolymer resin, is used. However, while high-temperature operation is desired in order to achieve size reduction and performance improvement of a fuel cell system, a polyethylene material whose thermal deformation temperature or continuous operation temperature is 100° C. or lower cannot secure reliability of the fuel cell. Japanese Patent Application Publication No. 2007-66766 (JP-A-2007-66766) discloses that a hot-melt adhesive, such as an acrylic adhesive, an olefin-based adhesive, etc., is used as an edge seal (corresponding to a protective layer portion). However, since the hot-melt adhesive has the property of melting at certain temperature, the thermal deformation temperature or the continuous operation temperature becomes low, so that reliability of the fuel cell cannot be secured as in the foregoing case of a polyethylene material.